1. Field of the Invention
The present invention relates to a dielectric ceramic (also called as “dielectric material” or “dielectric sintered body”, and in the present-description, called as “dielectric ceramic” hereafter), and in more particular, relates to such a dielectric ceramic excellent in sintering property at low temperatures and mechanical strength, and having excellent dielectric characteristics in GHz zone. The dielectric ceramic of the invention is broadly applicable as electronic parts. In particular, this is suited as electronic parts, wiring substrate mounting electronic parts thereon, among them multi-wiring substrates formed in multi-layers, and further as electronic parts for high frequency used in GHz zones, packages therefor or multi-wiring substrates (multi-layer wiring substrates or boards).
2. Description of the Related Art
The dielectric ceramic has conventionally been employed as various kinds of electronic parts or wiring substrates mounting them thereon. The dielectric ceramic used to such services has been demanded to be capable of being sintered at low temperatures as 1000° C. and have large mechanical strength. The dielectric ceramic having satisfied these requirements has mainly been made of glasses and an inorganic filler (the glasses: glass powder of softening point being about 500 to 800° C. and containing lead oxide, alkali earth metal oxide, alkali metal oxide and zinc oxide based on aluminoborosilicate) and (the inorganic filler: alumina, mullite, cordierite, titanic, forsterite, zirconia and quartz).
Such dielectric ceramics are disclosed in JP-A-53-60914, JP-A-60-235744, JP-A-63-239892, JP-A-3-33026, JP-A-7-135319 and JP-A-9-208258. Dielectric loss of these dielectric ceramics is 6×10−4 to 20×10−4 in MHz.
In recent years, it has particularly been demanded that the dielectric loss is small in the increasingly used GHz zone. Therefore, required dielectric ceramics are those which can be sintered simultaneously with low resistant conductors of Ag based metals and Cu based metals, are high in the mechanical strength, and less in warp, curve or camber (in this specification, it is sometimes simply referred to as warp) in sintered products (the less warp makes dimensional stability good, and can suppress transmission loss during using in the GHz zone).
However, it has been difficult to accomplish at the same ime the excellent sintering property at low temperatures and the mechanical strength, and the excellent dielectric characteristics in the GHz zone.